The present invention relates generally to the field of electronic devices and, in particular, the present invention relates to thermal management of electronic devices.
The current trends in microprocessor design are to increase their power, decrease their size, and increase their speed. This results in higher power in a smaller, faster microprocessor. Another trend is towards lightweight and compact electronic devices. As microprocessors become lighter, smaller, and more powerful, they also generate more heat in a smaller space, making thermal management a greater concern than before.
The purpose of thermal management is to maintain the temperature of a device within a moderate range. During operation, electronic devices dissipate power as heat. The heat must be removed from the device; otherwise, it will get hotter and hotter until it fails, reducing its service life. Short of failure, electronic devices run slowly and dissipate power poorly at high temperatures.
Naturally, heat moves from the device to the surrounding air and warms up the air by convection. The temperature at the surface of a heat-generating device is called the junction temperature. Heat is generated at the junction and must move from the junction to the surrounding or ambient air. Unfortunately, there is always some resistance to heat transfer, called thermal resistance. Basically, it is not easy to move heat from the device into the surrounding air. In fact, air is a rather good thermal insulator. Lowering the thermal resistance from the junction to the ambient air increases the power dissipation. To lower this thermal resistance, heat sinks are used.
An Integrated Vapor Chamber Heat Sink and Spreader
Current thermal designs do not have a sufficiently low thermal resistance to efficiently dissipate the heat generated by the new high power electronic devices. One such design for desktop and server computers is shown in FIG. 15. Two layers of thermal interface material 1508, 1510 between the die 1504 and the heat sink 1516 contribute a significant portion of the total thermal resistance. Also, the long distance between the die 1504 and the heat sink 1516 contributes to the high thermal resistance. There is a need for a new thermal design with a lower thermal resistance that can efficiently dissipate heat for high power electronic devices.
If the heat sink 1516 were put directly in contact with the die 1504, the thin lower wall of the heat sink 1516 would not have enough area available for heat transfer. Consequently, it would increase the thermal resistance internal to the heat sink 1516 and inefficiently dissipate heat. There is a need for a new thermal design that puts a heat sink directly in contact with the die and overcomes the problem of high internal thermal resistance.
Heat spreading is another problem introduced by putting a heat sink directly in contact with a die. Often there are xe2x80x9chot spotsxe2x80x9d on the die. Hot spots are spatial variations of power dissipation that increase the local temperature and cause malfunctions. Current thermal designs, such as the one shown in FIG. 15 have a heat spreader 1506 with inefficient heat spreading. There is a need for a new thermal design for desktop and server computers that eliminates the separate heat spreader, puts a heat sink directly in contact with the die, and spreads heat more uniformly.
An Embedded Direct Heat Pipe Attachment
Current designs for new high power mobile electronic devices, such as telephones, radios, laptop computers, and handheld devices do not efficiently dissipate the heat generated by these devices. One such design is shown in FIG. 16. The total thermal resistance is too high for effective power dissipation. One reason is that the heat pipe 1612 is too far away from the die 1604. Another reason is that the spreader plate 1608 lies between the heat pipe 1612 and the die 1604. There is a need for a new thermal design with low thermal resistance for effective power dissipation in mobile devices that embeds a heat pipe in a heat spreader and puts it in direct contact with the die.
In the prior art, applying forces 1614 at the corners of the spreader plate 1608 produces unbalanced loads that sometimes cause the spreader plate 1608 to tilt in various ways as it presses down on the thermal interface material 1606. This leads to large variations in the bond line thickness of the thermal interface material. These bond line thickness variations increase thermal resistance to an unacceptable level and reduce product reliability. There is a need for a new thermal design with central point loading over the center of the die resulting in uniform thickness of the thermal interface material and decreasing thermal resistance.
If a heat pipe is put in direct contact with the die, it must be protected from caving in under the pressure of the point load. There is a need for a new thermal design that embeds a heat pipe in a heat spreader so that the heat pipe is protected.